Forum home Commuter cycling forum Commuting general

Brompton chain slipping and new gear shifter question

bromptonitebromptonite Posts: 5
edited September 2016 in Commuting general
Hello all,

I have a couple of questions regarding my trusty Brompton that hopefully you wise folk can advise me on?

Recently the chain on my M3L has started to slip when I put it under strain (accelerating, going up hills, etc). I'm assuming something has worn out (the bike's about 2+ years old), but wonder if there is anything I could check first, in case it's root cause is something other than wear/tear?

If not, would you be able to advise what the likely cause is, and how I can remedy it? Chain/sprockets replacement? I am moderately mechanically savvy, and have taken the rear section of the Brompton to bits before (tyre replacement) so am 'comfortable' attempting a repair myself, with guidance from yourselves if it's on offer? Could you advise specifically what exact parts I will need, and if there are any good internet guides/videos out there that walk you through the process, which you can vouch for?

Additionally, I'm keen on replacing the gear shifter on my 3-speed Brompton, but am unsure as to what will be suitable. My bike has the standard Sturmey Archer SLS3C shifter ( ), and I would like to fit the DLS30 Dual Trigger shifter ( ) if feasible. I've emailed Sturmey Archer, and managed to coax out of them that the DLS30 Dual Trigger is compatible with the 3-speed hub. But they weren't able to confirm if it's compatible with a Brompton (!!). Does anyone have experience of this shifter, and can advise me as to its suitability please?

Thanks for taking the time to read my ramblings, and thanks in advance if you're able to offer me some Brompton wisdom related to the above.



  • keef66keef66 Posts: 13,123
    Get a chain wear checker and see if your chain's worn.
    Have a close look at the shape of the teeth on the chainring and the sprocket, see if they are looking decidedly shark-fin like.
    Is the chain tensioner still working properly?

    My guess is you need a new chain and possibly sprocket.
  • Thanks keef66. I don't have a chain wear checker, but also suspect it's the chain and/or sprocket being worn out. So I've ordered the following sprocket and chain (hoping I counted the number of teeth for the sprocket and chain-ring correctly):

    Brompton sprocket / disc set 13T for SRAM 3 speed: ... stack.html

    Brompton chain 98 Links 3/32" with PowerLink: ... in098.html

    I also discovered my 3-speed hub is a Sachs (aka SRAM), not a Sturmey Archer, so have ordered the SRAM T3 grip shifter to replace the standard shifter that came on the Brompton, hoping it is compatible ( ... ROKL5A1OLE )

    Finally, I've gone for some new handlebar grips - the Ergon GP1's, though I think they'll need cutting down (definitely on the grip shifter side) ( ... OPZG8B4IYM )

    I'll post updates/progress when I have any.
  • fenixfenix Posts: 5,437
    How many miles have you done on the Brompton in those two years ?
  • An educated guess would be 3500+ miles over the two years. But the bike was bought second hand, so it's likely irrelevant when it comes to the possible wear of the chain/sprocket, as I don't know if/when the chain/sprocket had been replaced or not before I bought it. I was told the Brompton had a full service prior to me buying it (visually this very much seemed the case - it looked new), but doubt this includes a chain and sprocket replacement as standard?!
  • shmoostershmooster Posts: 335
    Put a ruler against the chain and see if the 1/2" marks match up all the way along. If they don't your chains worn out. FWIW I've had worn out cassettes where I couldn't tell the difference from a new cassette but you can change the chain first and see if the cassettes worn after (ie if it still slips).
  • The RookieThe Rookie Posts: 27,811
    Id be very surprised if the chain wasn't worn and taken the front and rear sprockets with it on that mileage on a used bike.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • UPDATE: I've replaced the chain and rear sprocket and thankfully this seems to have fixed the slipping problem. The front chain-ring/sprocket doesn't seem to have been affected too much by the mileage. BUT I did make the mistake of ordering the wrong type of chain, so please learn from me not what to do. I ordered a 3/32" chain (as that's what was suggested for a 3-speed Brompton on the BrilliantBikes website), but in fact I needed a 1/8" chain (which is apparently standard for a fixed speed bike (which the 3-speed Brompton effectively is, as it uses a hub gear).

    Unfortunately when replacing the rear sprocket (which in itself was easy enough) I accidentally (stupidly) opened the hub and seem to have damaged some components. One is the sliding key that enables gear changes (a fragile rod that has been sheared in half). I've ordered a replacement part from Germany that should hopefully remedy that issue, I also suspect I have warped the bearing retainer just behind the sprocket, as there's a slight clunk when the wheel rotates now. But I don't conclusively know if this is the cause of the clunking or not. Any things that spring to mind that could be something other than the bearing retainer, before I order another replacement part?
Sign In or Register to comment.